This is a supplemental application to take advantage of a highly significant Quantitative Trait Locus (QTL) on chromosome 1 for high dose ethanol sensitivity that we have discovered in the Inbred Alcohol non- Tolerant (IANT) and the inbred Alcohol Tolerant (IAT rats) in spite of the fact that these animals were selectively bred for low dose effects. This QTL is in the same general location as one for this phenotype in the inbred High Alcohol Sensitive (IHAS) and inbred Low Alcohol Sensitive (ILAS) rats, but is much more significant and has a much higher heritability. We will take advantage of this unique opportunity to add to our knowledge of ethanol sensitivity by construction of congenic strains for the QTL, narrowing the region of the QTL and comparing the results to the same region in the I HAS and I LAS rats. We are also constructing congenic strains from the I HAS and I LAS rats on chromosomes 2 and 5. The QTL on chromosome 1 in the IHAS and ILAS rats is much smaller than in the IANT and IAT rats. These studies are important since among the risk factors for alcoholism in humans is a low initial sensitivity and/or rapid development of tolerance to ethanol. We have two animal models of this behavior, the rats selectively bred for high dose sensitivity (the IHAS and ILAS) and animals bred for low dose sensitivity (the IAT and IANT) [unreadable] [unreadable]